1. Field of the Invention
This invention relates generally to apparatus for studying the physical properties of particles carried in suspension and more particularly to such apparatus having a novel arrangement for initially filling an isolator tank forming a part of such apparatus with a predetermined desired level of clean electrolyte. The invention also relates to novel method and apparatus for obtaining particle analysis of a diluted sample produced with such apparatus.
2. Description of the Prior Art
The Parent Patent discloses an electrolyte supply system for particle measuring apparatus of the Coulter type in which an aperture retaining member is disposed in communication with a body of particulate liquid suspension to be tested. (The mark "Coulter" is the registered trademark, Registration No. 995,825 of Coulter Electronics, Inc. of Hialeah, Fla.). The aperture retaining member has an aperture to permit passage of the suspension from the body of liquid suspension into the member, and an inlet chamber for introduction of the particle free electrolyte which passes behind the aperture. As described, the structure of the Parent Patent deals with a specific problem which occurred during use of the so-called aperture tube disclosed in U.S. Pat. No. 3,299,354. The structure of U.S. Pat. No. 3,299,354 substantially decreased the possibility of undesirable spurious particle produced signals which sometimes occurred in prior art devices. The aperture tube was self-cleaning in that the suspension in the immediate vicinity of the aperture was kept relatively free of extraneous particles. Despite the self-cleaning aspect of the structure of U.S. Pat. No. 3,299,354, eddy currents of fluid in the aperture tube at the downstream end of the primary bore could occur, and these eddy currents could swirl into the secondary bore immediately adjacent the primary bore.
The structure of U.S. Pat. No. 3,746,976 (U.S. Reissue Pat. No. 28,558) improved on the structure of U.S. Pat. No. 3,299,354 with the addition of a pump device interposed between the first and second chambers of the aperture tube to produce a closed system in which there are no inlets or outlets other than the primary bore in the first chamber. In the structure of the Parent Patent, several configurations of aperture retaining members or tubes are disclosed in which the spurious signal producing zone of the aperture tube continuously is washed simultaneously with passage of the suspension through the aperture such that particles which have been sensed within the aperture and thereafter passed out of the same immediately are swept out of the spurious signal producing zone by particle free liquid which is moved in a passageway behind the aperture and thereafter to an outlet chamber. Application Ser. No. 573,265, entitled "Aperture Module" referred to herein, discloses an improved aperture retaining member incorporating the same wash or sweep flow of clean electrolyte behind the aperture to reduce the occurrence of undesirable spurious signals where they normally are produced.
In the system incorporating each of the aperture tubes of the Parent Patent and the aperture module of application Ser. No. 573,265, an electrolyte supply container or isolator is required to supply the clean electrolyte to wash behind the aperture. The operation of the Coulter device requires that the electrolyte supply chamber be electrically insulated from the aperture retaining member to prevent electrical interference with the particle sensing and measuring performed by the device. In the Parent Patent, the electrolyte supply container is provided with an electrical shield to partially serve this purpose. Additionally, the electrolyte introduced into the container is caused to drip across an air gap and pool at the bottom of the container to prevent completion of an electrical path through the container. It therefore is important that the level of electrolyte in the container initially is established to provide an air gap in the container and that the level does not rise in the container to close the air gap therein to enable completion of an electrical path through the container. It also is important, however, that the electrolyte level in the container does not drop to result in an empty condition thereof in which case maintenance of the important vacuum pressures in the Coulter device would be interrupted. The present invention is intended to provide a novel arrangement of restrictions in the electrolyte supply line on either side of the container to enable initial filling to a proper level of the container with electrolyte.
The microscopic particle sensing method performed with a Coulter device utilizes a particle sensing zone in which more than one particle might be present at any one time and thereby produce a coincidence condition. The particles pass through a minute scanning aperture or sensing zone wherein single particles are detected at a rate often well in excess of one thousand per second. Because of the physical parameters of the scanning aperture and the particle concentration coincidence of two particles in the aperture or zone at the same time or nearly the same time frequently occurs. As a result the effect is that one particle is sensed instead of two, although the amplitude of the resulting signal is proportional to the total of the particle sizes.
One method of correcting for this coincidence of particles simultaneously sensed is to apply a correction which is obtained from a computation using certain predetermined formulae. It is known, however, that the effect of coincidence is a function of concentration of the particles in the suspension to be tested. Decreasing the concentration to a point where coincident passage through the aperture or zone becomes negligible is therefore desirable. The invention also is intended to provide a method and structure whose end is to achieve a high dilution to decrease coincidence.